Steroselective synthesis of steroids and related compounds, part VI. [2+2+2]-cycloaddition of 4-hydroxy-substituted enediynes to 2-hydroxy-substituted decahydrophenanthrenes

Enediynes rac-4 were prepared in seven steps with an overall yield of 31% starting from 4-pentyn-l-ol (5). A cobalt mediated [2+2+2]-cycloaddition of these enediynes and subsequent removal of the metal fragment afforded the decahydrophenanthrenes rac-3/13 in 37-56% yield. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003).